1. Field of the Invention
The present invention relates to an image forming apparatus applied to a copying machine, a printer, a facsimile machine and the like and particularly to an image forming apparatus that performs image formation on a roll sheet.
2. Description of the Related Art
An electrophotography type image forming apparatus becomes widespread which transfers a toner image formed on a photoreceptor to a transfer material such as a sheet and fixes the toner image onto the sheet by heating/pressurizing the sheet on which the toner image has been transferred in a fixing portion.
The fixing portion used in such an image forming apparatus includes a fixing member constituted by a heating roller, for example, and a pressurizing member provided at a position facing the fixing member and constituted by a facing roller rotating in pressure contact with the fixing member side. A toner image is fixed onto the sheet by passage of a sheet carrying an unfixed toner image through a nip portion between the fixing member and the pressurizing member.
Conventionally, in the image forming apparatus, various measures have been taken for preventing winding of the sheet around the fixing member or the pressurizing member side in the fixing portion. In “bishub PRESS C7000 (by Konica Minolta, Inc.)”, for example, a configuration is adopted in which an actuator for detecting presence of a sheet is provided on a downstream side of the sheet in a conveying direction from the fixing portion in order to determine winding of the sheet around the fixing member. In the image forming apparatus, if the sheet is not detected by the actuator for a specified period of time, it is determined that the sheet has been wound around the fixing member.
Moreover, in Japanese Patent Laid-Open No. 2012-063743, in order to prevent jamming of the sheet wound around the fixing member by an adhesive force of the toner, a separation mechanism is provided which blows compressed air between the fixing member and the sheet so as to promote separation of the sheet from the fixing member.
On the other hand, in the electrophotography type image forming apparatus, a technology using a roll sheet as a transfer material is proposed (see Japanese Patent Laid-Open No. 2002-091237). In Japanese Patent Laid-Open No. 2002-091237, in order to solve a problem that curling tendency of the roll sheet becomes stronger as a remaining winding amount of the roll sheet reduces and thereby voids in transfer images tend to occur more easily, a configuration for controlling separation performance of the roll sheet from an image carrier in accordance with a remaining winding amount of the roll sheet is disclosed.